Effective, efficient ventricular pumping action depends on proper cardiac function. Proper cardiac function, in turn, relies on the synchronized contractions of the myocardium at regular intervals. When the normal cardiac rhythm is initiated at the sinoatrial node, the heart is said to be in sinus rhythm. However, when the heart experiences irregularities in the coordinated contraction of the myocardium, due to electrophysiologic disturbances caused by a disease process or from an electrical disturbance, the heart is denoted to be arrhythmic. The resulting cardiac arrhythmia impairs cardiac efficiency and can be a potential life threatening event.
In the supraventricular region of the heart, electrophysiologic disturbances are called supraventricular tachyarrhythmias (SVT). SVT can take several distinguishable forms, including paroxysmal atrial tachycardia, atrial flutter, or atrial fibrillation. SVT are self-sustaining process and may be paroxysmal or chronic.
The mechanisms behind these conditions are not well understood, but, generally, the electrical impulses that normally cause sinus rhythm are thought to progress repeatedly around irregular conduction pathways within the heart. These conditions, if uncontrolled, can become life threatening if the aberrant electrical impulses enter the atrioventricular node (AV node) in a sporadic and/or at an accelerated rate and cause an irregular ventricular rate that degenerates into an immediate life threatening ventricular arrhythmia.
Physicians have typically relied on the use of either pharmacological agents and/or electrical techniques to control paroxysmal or chronic SVT. Many acute SVT patients convert to sinus rhythm after receiving treatment with pharmacological agents. However, antiarrhythmic pharmacological agents can have undesirable adverse effects, particularly if the need for drug therapy is chronic.
Alternatively, physicians have used various electrical techniques to treat SVTs. The SVT most frequently treated in this manner is atrial fibrillation. If the atrial fibrillation is acute, the physician may attempt an electrical cardioversion. This technique has been effective in converting atrial fibrillation, but it can be quite a painful experience for the patient. Implantable atrial cardioverters have also been suggested as a potential treatment for atrial fibrillation. However, the use of these devices can still subject the patient to a very painful and traumatic experience. Furthermore, the energy these devices deliver in attempting to treat atrial fibrillation has the potential for causing transient shock-induced dysfunction as well as permanent damage to the tissue near the cardioversion electrodes.